The present invention generally relates to thermally compensated optical systems, and more particularly, to thermally compensated wavelength division demultiplexers and multiplexers and method of fabrication thereof.
The increasing demand for high-speed broadband communications has resulted in a rapid increase in fiber optic communications systems which require faster and more reliable components to interconnect associated optoelectronic devices of a network. These components may include devices for steering light beams through light transmissive mediums at specific angles. Currently, devices use opto-mechanical or electro-optical technology to steer light beams to a specified angle.
Problems which may occur in optical components include performance degradation due to variances in temperature. Optical components may be used in several different environments which may require components or systems that are intolerant to changes in temperature. In wavelength-division multiplexers and demultiplexers, characteristics that may alter as the temperature changes include channel bandpass, channel central wavelengths, polarization-dependent loss (PDL), and channel insertion losses.
Lens materials possess both a coefficient of thermal expansion and a temperature derivative of refractive index. Thus one cannot merely use zero-expansion lens materials unless these materials also have refractive indices that are invariant with temperature. Mirror systems, on the other hand, do have optical properties that are independent of temperature, provided the mirrors and the support structure are all made with zero-expansion glass.
Some systems use a coaxial two-mirror all-reflecting lens. However, there is a transmission loss caused by the central obscuration. Another possibility is the use of off-axis mirrors, as is commonly done in the well-known Czerny-Turner and Ebert spectrometers. These mirror configurations may increase the size of the device over that of a coaxial system, and have not been seriously considered for use.
In accordance with teachings of the present invention, a thermally compensated optical device is provided. The optical device includes a diffraction grating having a substantially zero temperature coefficient and a grating mount having a temperature coefficient coupled to the diffraction grating. The device further includes a lens assembly coupled to a lens mount having a temperature coefficient and operable to communicate optical signals between the lens assembly and the diffraction grating. The lens assembly includes a lens element having a thermal derivative of refractive index based on the temperature coefficient of the lens mount.
In accordance with another aspect of the present invention, a thermally compensated optical system is provided. The system includes a lens mount having a temperature coefficient and operable to position a lens assembly within an optical path. The system further includes a fiber mount operable to position an optical fiber at a thermally compensated distance relative to the lens assembly. The optical fiber mount includes a substantially similar temperature coefficient as the lens mount and the fiber mount is positioned relative to the optical lens mount such that a focal plane of the lens assembly is maintained at the optical fibers in response to a temperature variation.
In accordance with another aspect of the present invention, a thermally compensated optical system is provided. The system includes a diffraction grating coupled to a grating mount having a temperature coefficient. The system further includes an optical fiber coupled to a fiber mount and the fiber mount having a fiber mount temperature coefficient. The system further includes a lens assembly coupled to a lens mount. The lens mount was a substantially similar temperature coefficient to the fiber mount, and the lens assembly is positioned between the fiber mount and the grating mount.
In accordance with another aspect of the present invention an optical network for communicating information embodied within an optical signal is provided. The network includes a thermally compensated optical device operable to communicate information between an initiating point and a destination point. The device includes a lens mount operable to position a lens assembly within an optical path and the lens mount includes a temperature coefficient. The device further includes a fiber mount operable to position an optical fiber at a thermally compensated distance relative to the lens assembly and the optical fiber mount includes a substantially similar temperature coefficient as the lens mount. The fiber mount is positioned relative to the optical lens mount such that a focal plane associated with the optical fiber mount is maintained in response to a temperature variation.
In accordance with another aspect of the present invention a method of fabricating a thermally compensated optical device is disclosed. The method includes coupling a diffraction grating to a grating mount and the diffraction grating includes a substantially zero temperature coefficient. The method includes coupling a fiber mount plate to a fiber mount wherein the fiber mount plate includes a fiber mount temperature coefficient. The method also includes positioning a lens assembly between the grating mount and the fiber mount such that the lens assembly communicates optical signals between the lens assembly and the diffraction grating. The method further includes coupling a lens element to the lens assembly, the lens element including an expansion coefficient, a refractive index and thermal derivatives of index based on the temperature coefficient of the base plate.
It is a technical advantage of the present invention to provide a thermally compensated WDDM module having a wide thermal operating range.
It is a further technical advantage of the present invention to provide a demultiplexer having insertion loss that is substantially invariant to changes in temperature.
It is another technical advantage of the present invention to provide a WDDM module having thermally matched optical elements and mounting fixtures.
It is another technical advantage of the present invention to provide a thermally compensated WDDM module that uses a zero-expansion optical grating.
It is another technical advantage of the present invention to provide a fiber optic mount and lens mount having substantially similar temperature coefficients such that the fiber mount and lens mount are coaxial with each other as the temperature varies.
It is a further technical advantage of the present invention to provide a refractive lens that minimizes thermal variations in lens back focal length thereby maintaining a focal plane for optically coupled optical fibers as the temperature varies.